review of g in dis and pp … a lot has happened since kyoto frank ellinghaus university of mainz /...

Review of G in DIS and pp… a lot has happened since Kyoto

Frank Ellinghaus

University of Mainz / University of Colorado

October 2008

SPIN’08, Charlottesville, USA

Frank Ellinghaus, Spin’08, Charlottesville

e-p Spins antialigned

In the beginning….

– Electron polarization transfers to virtual photons– Compare DIS cross sections with aligned and antialigned ep spins

e-p Spins aligned~

g1 (proton) > 0-> Larger cross section for anti-aligned ep Spins -> Higher probability for aligned quark-proton Spins

212( , )B

B

dg x Q

dx dQ

• Polarize electrons and nucleons (started in mid 1970s at SLAC)

G. Baum et al, PRL 51, 1983


Results from Inclusive Polarized DIS

• Analogous to unpolarized (F2) case, g1 can be used to fit polarized PDFs:

Polarized PDFs extracted from fits to g1(proton, deuteron)

• Result: Quarks carry only 30% of the nucleon spin (0.3)

HERMES: PRD 75:012007 (2007)

COMPASS: PLB 647:8 (2007)

• Gluon contribution G not well constrained due to small range in xB,Q2 (no polarized ep collider)

( ), ( ), ( )B B Bq x q x G x

…try DIRECT measurements ->


G via direct measurement in DIS

||

1 1~ ( ) ...PGF PGF BG BGG

A

f a fGf A A

Photon-Gluon Fusion: * g -> qqbar

• ccbar production, detect D-mesons, hard scale provided by charm mass, clean channel (low BG), statistically limited

• detect hadrons (or hadron pairs) with Q2>1 GeV2(hard scattering) More BG sources with difficult to determine or/and model-dependent fractions and asymmetries. Larger sample…

• detect hadrons (or hadron pairs) using all Q2

Even more BG sources with difficult to determine or/and model-dependent fractions and asymmetries. Largest sample…


Fixed Target DISBeam: 27.6 GeV e+/e-; Beam: 27.6 GeV e+/e-; 50-55% polarization50-55% polarization

Target: H, D Target: H, D 80-85% polarization80-85% polarization

6/30/07

Beam: 160 GeV Beam: 160 GeV ; ; 75-80% polarization75-80% polarization

Target: Target: 66LiD; LiD; 50% polarization50% polarization


The “golden” channel

D*->D0 soft

2002-2004 analysis: hep-ex/0802.2160

F. KunneTuesday

2002-2006 preliminary analysis:

“tagged D0”


COMPASS: Hadron Pairs, Q2 > 1 (GeV/c)2

LEPTO with JETSET tuned to data…

• pT>0.7 GeV/c for both hadrons increases PGF contr.• Q2 > 1 (GeV/c)2 provides hard scale• At least two add. subprocesses to be considered

500k events

K. KurekTuesday


COMPASS: Hadron Pairs, Q2 < 1 (GeV/c)2

0.080.040.095gx

PYTHIA

Add. Sensitivity to G, but polarized PDFs of photon unmeasured

• pT>0.7 GeV/c for both hadrons increases PGF contr.• pT

2 > 2.5 (GeV/c)2 provides hard scale

• Add. contr. (about 50%) from resolved-photon processes

PGF

QCDC

LO

PLB 633 (2005) 25

preliminary2 23( / )GeV c


HERMES, hadrons, all Q2

PYTHIA (tuned to data)

2 0.1250.082/ ( , ) 0.078 0.034 0.011g g x

20.204 1.35 2 GeVx

Results from different (proton, deuterium) data samples and different event topologies are consistent.

Good sensitivity, but model dependentg/g=0 -> contribution of quarks


Summary Direct DIS measurements

g/g=0 is likely small with unknown sign!


RHIC @ BNL

STARSTAR

Relativistic Heavy Ion Collider also provides longitudinally and transverselypolarized proton beams at s = 200 GeV, 62.4 GeV, (500 GeV, 2009+)

Polarimeter (H jet) pC Polarimeters

Spin Rotators Siberian Snakes


PHENIX and STAR

Large acceptanceAzimuthal symmetry

High rate capabilityLimited acceptance


PHENIX longitudinally polarized pp Runs

Year s [GeV] Recorded L Pol [%] FOM (P4L)

2003 (Run-3) 200 .35 pb-1 27 1.5 nb-1

2004 (Run-4) 200 .12 pb-1 40 3.3 nb-1

2005 (Run-5) 200 3.4 pb-1 49 200 nb-1

2006 (Run-6) 200 7.5 pb-1 57 690 nb-1

2006 (Run-6) 62.4 .10 pb-1 48 5.3 nb-1

(Similar numbers for STAR. Experiments can separately choose longitudinal or transverse polarization.)


G via direct measurement in pp

2 2~LL gg qg qqA a a q G aG q

Access to polarized gluon distribution function via double helicity asymmetry in inclusive polarized pp scattering, e.g.,

Invariant mass spectrum of 2 photons in EMCal(M=135MeV)

Measure from DISpQCD, fragmentation fcts.

0p p X

NRN

NRN

PPA

YBLL

1

L

LR Relative Luminosity R using

beam-beam counters


First: Check unpolarized case!

Using a set of unpolarized PDFs ( + fragmentation functions in case of hadron (0) production) the cross section agrees with NLO pQCD calculations.

PHENIX -- 0

PRD76:051106,2007

STAR -- jets

PRL 97, 252001 (2006)


STAR -- jetsRun 6 preliminary

Run 5 (2005): PRL 100, 23 (2008)

• G = G(x), -G(x) excluded;• GRSV-std excluded with 99% CL

Run 6 preliminary

M. SarsourFriday

• No inconsistency with DIS data due to generally large uncertainties on Dg(x).• Small or negative gluon contribution to nucleon spin favored in this model.• Data also consistent with GS-C ->


Model dependence of G

g integral between

GRSV

- 0

GRSV

- std

GS-C

0<x<1 0 0.4 1

0.02<x<0.3 0 0.25 0

• Measurement averages over certain x range• Shape of G(x) cannot be extracted -> Value for first moment model dependent


PHENIX --0 at 200 GeV

Run 5: Phys.Rev.D76:051106,2007Run 6: arXiv:0810.0694

GRSV: Glueck et al., PRD 63 (2001)

G = G(x), -G(x) excluded; GRSV-std slightly disfavored

K. NakanoTuesday

Run 5 + Run 6


STAR – 0, PHENIX – PHENIX J/Psi

PHENIX excludes G= G(x), -G(x)

J. Seeletoday

STAR 0 consistent with PHENIX

X. WangFriday

A. Hoffman

today


+, –, 0 and the sign of G

0

0 LL LL LLG A A A

0

d d dD D D

0

0 LL LL LLG A A A

Especially in the region where qg scattering is dominant (pT > 5 GeV),the increasing contribution of d quarks (d<0) leads to:

“Model independent” conclusion possible once enough data is available.

Fraction of pion production

s=62.4 GeV

PHENIX Preliminary

A. Dattatoday

A. MorrealeTuesday


Charged hadrons at STAR A. Kocoloskitoday


Direct Photons at s=200 GeV

Run-5

At the end of the day all these (and the DIS, SIDIS) asymmetry data need to go into a “global” QCD fit in order to extract G! ->

q

g q-> small unc. from FFs-> better access to sign of G (q times G)

Theoretically clean “Golden Channel” is luminosity hungry…

Dominated by qg Compton:

R. Bennetttoday


First pol. PDF extraction using pp data

DSSV, arXiv: 0804.0422First “global” (DIS+SIDIS+pp) analysis!

G small in measured range (0.05 < x< 0.2).Contribution at small or large x?

Different ranges in x can be probed in:• 500 GeV (2009+, lower x) and 62 GeV running (larger x, larger scale unc.) ->• different rapidities ->

• Strong impact of Star jets and Phenix 0 in measured range. • Shape of G(x) cannot be extracted -> All “missing” spin can be at low x…. • Next step: Mapping of x-dependence via di-jets, di-hadrons and gamma-jet

M. StrattmannTuesday


• At fixed xT = 2pT/sqrt(s) cross-section is 2 orders of magnitude higher at 62.4GeV than at 200GeV

• Significant result at high xT from small data set at 62.4 GeV (0.04 pb-1) when compared to 200 GeV data (1.8pb-1)

• pQCD applicable for pT > 2 GeV/c…

Accessing different x-rangesPHENIX: 0 ALL at s=62.4 GeV

Increased sensitivity to larger x

K. NakanoTuesday

STAR: 0 ALL at forward rapidity

Increased sensitivity to smaller x

• Also: step towards gamma-jet correlation measurements to map out the x-dependence• STAR Di-Jet measurements promising

T. SakumaFriday

S. WissinkFriday

arXiv: 0810.0701


Summary & Outlook• PHENIX and STAR data provided a significant constraint on the

polarized gluon PDF in a global QCD fit to “all” DIS, SIDIS and pp data

-> G(x) small in measured range (0.05 < x < 0.2)• Direct measurements by HERMES+COMPASS support this finding with

somewhat larger uncertainties.• No sensitivity to shape of G(x)

-> all the “missing” spin can still be at smaller x.

• HERMES: – final word (long paper) soon

• COMPASS: – Open Charm: Add 2007 data (small improvement)

– High-pT hadrons, Q2>1 (GeV/c)2: Add 2006+2007 data (significant improvement)

• PHENIX+STAR: – Different beam energies (500 GeV, 2009+) and rapidities will give access to an

order of magnitude smaller x

– Correlation measurements will provide sensitivity to shape of G(x)

review of g in dis and pp … a lot has happened since kyoto frank ellinghaus university of mainz /...

Documents

charlottesville g

polarization slide

charlottesville compass

charlottesville results

charlottesville hermes

preliminary slide

charlottesville ep spins

charlottesville rhic